The present invention relates to a torsion bar assembly for a vehicle suspension system, and more particularly to modifying the effective length of the torsion bar to provide variable effective spring rates.
Vehicles are commonly equipped with independent suspension systems which can include a vibration or shock absorbing device for absorbing road shock and other vibrations while providing a smooth and comfortable ride for the vehicle occupants. One type of shock absorbing system includes a torsion bar. In suspension systems of this type, the torsion bar extends longitudinally along the length of the vehicle. One end of the torsion bar is connected to a suspension control arm while the other end is fixed to the vehicle frame. The torsion bar twists according to the articulation of the suspension component to provide a torsional elastic resistance to the up/down or jounce/rebound movement of the suspension component. The torsion bar thereby acts as a spring to absorb vibrations from the road surface and provide particular handling qualities.
As noted, one end of the torsion bar is attached to the vehicle frame. It is known to provide an adjuster arm to connect the end of the torsion bar to the frame. The adjuster arm allows the torsion bar to be preloaded or twisted to provide a particular spring rate of the torsion bar and thereby tune the suspension characteristics. However, such conventional torsion bar systems are limited to the predefined constant spring rate.
It is also known to provide a multi-segment torsion bar. Each segment has a different diameter to provide different spring rigidities. A catching protrusion is located at the boundary between each segment. When the torsion bar is subjected to small scale vibrations, the small diameter segment twists and absorbs the vibration. When vibration generate twisting of the torsion bar in excess of the catching protrusion, the small diameter segment becomes rotationally fixed and the relatively larger diameter segment twists to absorb the vibration. However, such a multi-segmented torsion bar is difficult to manufacture as each segment must be securely attached to the other segments to resist the torsional loads. Further, the multi-segment torsion bar is predefined during manufacture to provide particular spring rates based on the diameter and length of the connected segments. This limits the adaptability of the torsion bar and necessarily prevents later fine tuning of the suspension system as the segments are fixed.
Accordingly, it is desirable to provide a torsion bar suspension, which is relatively uncomplicated to manufacture, and which can provide variable spring rates in a multiple of vehicle applications. It is also desirable to provide a torsion bar suspension which can be fine-tuned after installation in a vehicle.
The suspension system according to the present invention includes a one-piece torsion bar having at least one adjuster arm. The adjuster arms are mountable along the length of the torsion bar to contact respective stop members. The adjuster arms contact the stop members when the torsion bar is subjected to a predetermined torsion. That is, the entire torsion bar can be twisted until the predetermined torsion is reached and a first adjuster arm contacts a first stop. When the first adjuster arm contacts the first stop, a portion of the torsion bar is rotationally fixed and the effective length of the torsion bar is reduced. By reducing the effective length of the torsion bar, the effective spring rate of the torsion bar is increased. Further, by axially shifting the adjuster arms after installation in the vehicle, the spring rates of the torsion bar and thus the suspension system can be fine-tuned.
According to the present invention, relatively small vibrations, such as that which occur during a normal straight travelling condition, are absorbable by the entire torsion bar. Because the entire length of the torsion bar is the effective length, a relatively soft spring constant absorbs the vibrations and provides a smooth ride. However, as impact or additional loads are applied to the torsion bar, the effective length of the torsion bar is reduced and the suspension is stiffened.
The present invention therefore provides a suspension system for a vehicle which can enhance riding comfort and handling by modifying the effective length of the torsion bar to achieve multiple spring constants with a single constant diameter torsion bar.